Sabit ve değişken genlikli DGM dalgaları ile beslenen asenkron makina performans etüdü

Abstract

The output voltage waveforms of ideal inverters should be sinusoidal. However, the waveforms of practical inverters are nonsinusoidal and contain some time harmonics. These time harmonics causes additional losses which decrease the efficiency of induction machine. The effects of time harmonics have to be analysed in order to increase the performance of induction machines. The performance of an induction machine when subjected to a nonsinusoidal voltage waveform has been analysed by many authors. It has been found that the destructive effects of the time harmonics decrease the efficiency of the drive system due to increased additional losses. Many authors have worked upon the construction of waveforms and inverter electronics to eliminate the low order harmonics which cannot be filtered by the machine impedance. These works have been become succesful and found practical applications.In [ 19 ], it was shown that the effects of PWM strategy upon the performance characteristics of optimised total harmonic distortion. A sample modulating wave and triangular earner wave were used for modulating technique and intersection of them were employed to produce the switching edges of PWM wave at the output of the inverter. While in [ 23 J, the crest factor of the current waveform induced by a PWM sequence was used as a measure of its optimality and shown that 250 - 300 Hz switching frequency region would he preferable. Analytical and experimental investigation on steady state and transient behavior of an induction motor fed from nonsinusoidal power supplies is presented in f 16 ]. The analytical investigations are based on a direct three phase model developed for this purpose. Simulation procedure for computing the exact nature obtained from a pulse width modulated ( PWM ) inverter is desoribed. Transient studies exhibiting the effects of specific PWM pattern changing on the induction motors are outlined. The ability of the developed model to represent faulty inverter conditions such as single phasing is described and analysed. Finally key results are verified experimentally on a PWM inverter fed induction motor. The total losses of an induction motor were calculated by using superposition of separate harmonic currents and voltage effects. The losses of the rotor and the stator were separately estimated and combined for frequencies from 100 to 20000 Hz. The loss model of the motor was developed and define as the function of frequency for different power ratings by using empirical datas obtained experimentally in [ 14 J. While in [ 15 ], the analysis of torque generation were dedicated in the induction machines. The general conditions concerning the existance of synchronous and asynchronous torques were presented. The results of XIthat analysis were illustrated by numerical examples and verified with experimental investigation. The modified equivalent circuit and the present torque analysis are general for the specialist in asynchronous machines who can handle them without any complications. In I 9 ], traditional PWM AC motor drives perform well over a large speed range and have many positive features demostrated with their simplicity. However, the waveforms used are significantly less than ideal at high modulation depths and low switching rates, especially with regard to harmonically induced motor losses. An developed strategy for digitally producing PWM based on simple triangulation methods is presented. A new technique for the decreasing the harmonic losses resulting from sinusoidal PWM waveforms is analysed in depth and realised on a 40 kVA inverter. Tests with this inverter on 7,5 kW and 15 kW motors confirm that the inverter's performance is significantly enhanced for certain operating conditions without any significant sacrifies. On the other hand, in reference [ 12 ], a new PWM algorithm for battery-source three - phase inverters is described. The concept of the algorithm is to determine the pulse widths by equating the areas of the segments of the sinusoidal referances with the related output pulse areas. The algorithm is especially suitable to handle a non - constant voltage source with good harmonic suppresion. Since the pulse widths are computable in real time width minimal storage requirement as well as compact hardware and software. XllIt is particularly suitable for single - chip microcomputer Intel 8095 - based battery source inverter can control a 3 kW synchronous motor drive satisfactorily over a frequency range of 2 to 100 Hz. In references [ 8 J, [ 18 ] and [ 22 J PWM voltage waveforms were analysed for a motor drive application. The switching patterns were developed in single and three - phase half - bridge inverters. The approach was based upon the minimising the harmonic content of the current flowing into the motor. In [ 8 ], [ 13 J and [ 17 ] harmonic elimination methods have been discussed in PWM voltage waveforms for an AC motor - drive using a six - thyristorised full - bridge inverter. In [ 10 ], it was shown that the hysterisis and eddy - current losses which produced in an AC machine, when subjected a nonsinusoidal voltage, as PWM, have changed with pulse duration. Although, the amount of change was insignificant in hysterisis losses, there was a substantial increase in eddy - current losses. PWM waveforms were analysed and obtained loss - optimal PWM waveforms for variable speed induction motor drives. PWM waveforms were introduced differently and novel waveforms were demonstrated. Effects of supply voltage waveforms upon iron losses were examined in an induction motor in references [ 11 ], ( 20 ] and [ 21 J. XlllIn this study, firstly the construction of nonsinusoidal waveforms is analysed. Two types of PWM voltage waveforms have been formed,one of which had oonstant pulse amplitude, while the other had variable amplitude. Harmonic contents of these waveforms were analysed and harmonic percentages are given in section 3. The performance analysis of induction machines fed by PWM of oonstant amplitude ( CAPWM ) and PWM of variable amplitude ( VAPWM ) had were given in section 4. The losses occurred in stator and rotor of a slip - ring and a squirrel - cage machines were analysed and compared for a selected frame size. The machine performances obtained for the frequency range of 1 Hz to 100 Hz. Hence the best performances of machines were obtained for used PWM waveforms. The method of selecting a proper PWM waveform was discussed in section 5 to obtain the best performance of an induction machine.